diff mbox

[v1,8/9] target-arm: A64: Create Instruction Syndromes for Data Aborts

Message ID 1455287642-28166-9-git-send-email-edgar.iglesias@gmail.com
State New
Headers show

Commit Message

Edgar E. Iglesias Feb. 12, 2016, 2:34 p.m. UTC 
From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>

Add support for generating the instruction syndrome for Data Aborts.
These syndromes are used by hypervisors for example to trap and emulate
memory accesses.

We save the decoded data out-of-band with the TBs at translation time.
When exceptions hit, the extra data attached to the TB is used to
recreate the state needed to encode instruction syndromes.
This avoids the need to emit moves with every load/store.

Based on a suggestion from Peter Maydell.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
---
 target-arm/cpu.h           |  5 +++-
 target-arm/op_helper.c     | 34 +++++++++++++++++++++++--
 target-arm/translate-a64.c | 63 +++++++++++++++++++++++++++++++++++++++++++++-
 target-arm/translate.c     |  5 +++-
 target-arm/translate.h     |  3 +++
 5 files changed, 105 insertions(+), 5 deletions(-)

Comments

Peter Maydell Feb. 16, 2016, 7:13 p.m. UTC | #1 
On 12 February 2016 at 14:34, Edgar E. Iglesias
<edgar.iglesias@gmail.com> wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>
>
> Add support for generating the instruction syndrome for Data Aborts.
> These syndromes are used by hypervisors for example to trap and emulate
> memory accesses.
>
> We save the decoded data out-of-band with the TBs at translation time.
> When exceptions hit, the extra data attached to the TB is used to
> recreate the state needed to encode instruction syndromes.
> This avoids the need to emit moves with every load/store.

I think this patch also would be simpler if the encoded info
put in with the TBs was just the syndrome register, rather
than some other encoding.

thanks
-- PMM
Edgar E. Iglesias Feb. 18, 2016, 9:56 a.m. UTC | #2 
On Tue, Feb 16, 2016 at 07:13:32PM +0000, Peter Maydell wrote:
> On 12 February 2016 at 14:34, Edgar E. Iglesias
> <edgar.iglesias@gmail.com> wrote:
> > From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>
> >
> > Add support for generating the instruction syndrome for Data Aborts.
> > These syndromes are used by hypervisors for example to trap and emulate
> > memory accesses.
> >
> > We save the decoded data out-of-band with the TBs at translation time.
> > When exceptions hit, the extra data attached to the TB is used to
> > recreate the state needed to encode instruction syndromes.
> > This avoids the need to emit moves with every load/store.
> 
> I think this patch also would be simpler if the encoded info
> put in with the TBs was just the syndrome register, rather
> than some other encoding.

My first try was to only pass the bits needed for the iss
(i.e not the full data abort syndrome). We don't have all
the info needed at translation time to create the full
syndrome (e.g stage2 trap? stage2 trap while stage1 PTW, etc).

But we could maybe create as much of the data abort syndrome
as possible at translation time and then have the exception
handling code add the missing bits. We can then pass the
preliminary syndrome from translation time to exception time
in the std syndrome format. I can have a look and see what I
can do if that makes more sense.

Thanks,
Edgar
Peter Maydell Feb. 18, 2016, 11:42 a.m. UTC | #3 
On 18 February 2016 at 09:56, Edgar E. Iglesias
<edgar.iglesias@gmail.com> wrote:
> On Tue, Feb 16, 2016 at 07:13:32PM +0000, Peter Maydell wrote:
>> I think this patch also would be simpler if the encoded info
>> put in with the TBs was just the syndrome register, rather
>> than some other encoding.
>
> My first try was to only pass the bits needed for the iss
> (i.e not the full data abort syndrome). We don't have all
> the info needed at translation time to create the full
> syndrome (e.g stage2 trap? stage2 trap while stage1 PTW, etc).
>
> But we could maybe create as much of the data abort syndrome
> as possible at translation time and then have the exception
> handling code add the missing bits. We can then pass the
> preliminary syndrome from translation time to exception time
> in the std syndrome format. I can have a look and see what I
> can do if that makes more sense.

Yep, that was basically what I had in mind.

Am I right in thinking that at translate time we capture:
 IL ISV SAS SSE SRT SF AR
and then at exception time we determine:
 EC FnV EA CM S1PTW WnR DFSC
?

In that case I think you could reasonably have the info stored
with the TBs be "template syndrome >> 14" (since bits [13:0] are
all info determined at exception-time). The only reason for doing
this is that the encoded data is stored as sleb128 deltas between
lines so keeping the values numerically smaller should make them
take up a bit less space. (I have no idea how significant the
space saving would be.)

You should then be able to just have restore_state_to_opc()
write straight to env->exception.syndrome rather than needing
a new field in the cpu state.

thanks
-- PMM
Edgar E. Iglesias Feb. 19, 2016, 1:12 p.m. UTC | #4 
On Thu, Feb 18, 2016 at 11:42:17AM +0000, Peter Maydell wrote:
> On 18 February 2016 at 09:56, Edgar E. Iglesias
> <edgar.iglesias@gmail.com> wrote:
> > On Tue, Feb 16, 2016 at 07:13:32PM +0000, Peter Maydell wrote:
> >> I think this patch also would be simpler if the encoded info
> >> put in with the TBs was just the syndrome register, rather
> >> than some other encoding.
> >
> > My first try was to only pass the bits needed for the iss
> > (i.e not the full data abort syndrome). We don't have all
> > the info needed at translation time to create the full
> > syndrome (e.g stage2 trap? stage2 trap while stage1 PTW, etc).
> >
> > But we could maybe create as much of the data abort syndrome
> > as possible at translation time and then have the exception
> > handling code add the missing bits. We can then pass the
> > preliminary syndrome from translation time to exception time
> > in the std syndrome format. I can have a look and see what I
> > can do if that makes more sense.
> 
> Yep, that was basically what I had in mind.
> 
> Am I right in thinking that at translate time we capture:
>  IL ISV SAS SSE SRT SF AR
> and then at exception time we determine:
>  EC FnV EA CM S1PTW WnR DFSC
> ?

Yes. It gets a little messy due to the need to the clearing
of ISV (and related fields) and thus setting IL, if the abort
does not target EL2 but it's not too bad.

> 
> In that case I think you could reasonably have the info stored
> with the TBs be "template syndrome >> 14" (since bits [13:0] are
> all info determined at exception-time). The only reason for doing
> this is that the encoded data is stored as sleb128 deltas between
> lines so keeping the values numerically smaller should make them
> take up a bit less space. (I have no idea how significant the
> space saving would be.)
> 
> You should then be able to just have restore_state_to_opc()
> write straight to env->exception.syndrome rather than needing
> a new field in the cpu state.

Sounds good!

Thanks!
Edgar
diff mbox

Patch

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index a00a121..fecc48f 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -95,7 +95,7 @@ 
 struct arm_boot_info;
 
 #define NB_MMU_MODES 7
-#define TARGET_INSN_START_EXTRA_WORDS 1
+#define TARGET_INSN_START_EXTRA_WORDS 2
 
 /* We currently assume float and double are IEEE single and double
    precision respectively.
@@ -196,6 +196,9 @@  typedef struct CPUARMState {
     uint32_t condexec_bits; /* IT bits.  cpsr[15:10,26:25].  */
     uint64_t daif; /* exception masks, in the bits they are in PSTATE */
 
+    /* IS state from decoded instructions. Only valid after Data aborts.  */
+    ARMInsnSyndrome isyn;
+
     uint64_t elr_el[4]; /* AArch64 exception link regs  */
     uint64_t sp_el[4]; /* AArch64 banked stack pointers */
 
diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
index 9bf635f..b195848 100644
--- a/target-arm/op_helper.c
+++ b/target-arm/op_helper.c
@@ -115,8 +115,23 @@  void tlb_fill(CPUState *cs, target_ulong addr, int is_write, int mmu_idx,
             syn = syn_insn_abort(same_el, 0, fi.s1ptw, syn);
             exc = EXCP_PREFETCH_ABORT;
         } else {
+            if (target_el != 2 || fi.s1ptw) {
+                /* ISV is only set for data aborts routed to EL2 and
+                 * never for S1PTWalks faulting on Stage 2.
+                 *
+                 * See ARMv8 specs:
+                 * ISS encoding for an exception from a Data Abort, the
+                 * ISV field.
+                 */
+                env->isyn.dabt.valid = 0;
+            }
             syn = syn_data_abort(same_el,
-                                 0, 0, 0, 0, 0, 0,
+                                 env->isyn.dabt.valid,
+                                 env->isyn.dabt.sas,
+                                 env->isyn.dabt.sse,
+                                 env->isyn.dabt.srt,
+                                 env->isyn.dabt.sf,
+                                 env->isyn.dabt.ar,
                                  0, 0, fi.s1ptw, is_write == 1, syn,
                                  env->thumb);
             if (is_write == 1 && arm_feature(env, ARM_FEATURE_V6)) {
@@ -163,9 +178,24 @@  void arm_cpu_do_unaligned_access(CPUState *cs, vaddr vaddr, int is_write,
         env->exception.fsr |= (1 << 11);
     }
 
+    if (target_el != 2) {
+        /* ISV is only set for data aborts routed to EL2 and
+         * never for S1PTWalks faulting on Stage 2.
+         *
+         * See ARMv8 specs:
+         * ISS encoding for an exception from a Data Abort, the
+         * ISV field.
+         */
+        env->isyn.dabt.valid = 0;
+    }
     raise_exception(env, EXCP_DATA_ABORT,
                     syn_data_abort(same_el,
-                                   0, 0, 0, 0, 0, 0,
+                                   env->isyn.dabt.valid,
+                                   env->isyn.dabt.sas,
+                                   env->isyn.dabt.sse,
+                                   env->isyn.dabt.srt,
+                                   env->isyn.dabt.sf,
+                                   env->isyn.dabt.ar,
                                    0, 0, 0, is_write == 1, 0x21,
                                    env->thumb),
                     target_el);
diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
index 9e26d5e..2f17cba 100644
--- a/target-arm/translate-a64.c
+++ b/target-arm/translate-a64.c
@@ -1803,6 +1803,24 @@  static void gen_store_exclusive(DisasContext *s, int rd, int rt, int rt2,
 }
 #endif
 
+static void disas_ldr_update_isyn_sse_sf(DisasContext *s, int size,
+                                        bool is_signed, int opc)
+{
+    int opc0 = extract32(opc, 0, 1);
+    int regsize;
+
+    s->isyn.dabt.sse = is_signed;
+    /* Update the Sixty-Four bit (SF) registersize. This logic is derived
+     * from the ARMv8 specs for LDR (Shared decode for all encodings).
+     */
+    if (is_signed) {
+        regsize = opc0 ? 32 : 64;
+    } else {
+        regsize = size == 3 ? 64 : 32;
+    }
+    s->isyn.dabt.sf = regsize == 64;
+}
+
 /* C3.3.6 Load/store exclusive
  *
  *  31 30 29         24  23  22   21  20  16  15  14   10 9    5 4    0
@@ -1859,6 +1877,12 @@  static void disas_ldst_excl(DisasContext *s, uint32_t insn)
         } else {
             do_gpr_ld(s, tcg_rt, tcg_addr, size, false, false);
         }
+
+        /* Generate ISV for non-exclusive accesses including LASR.  */
+        s->isyn.dabt.valid = true;
+        s->isyn.dabt.sse = false;
+        s->isyn.dabt.sf = size == 3 ? 64 : 32;
+        s->isyn.dabt.ar = is_lasr;
     }
 }
 
@@ -1901,6 +1925,11 @@  static void disas_ld_lit(DisasContext *s, uint32_t insn)
         }
         size = 2 + extract32(opc, 0, 1);
         is_signed = extract32(opc, 1, 1);
+
+        /* Enable ISV generation.  */
+        s->isyn.dabt.valid = true;
+        s->isyn.dabt.sse = is_signed;
+        s->isyn.dabt.sf = size == 3 ? 64 : 32;
     }
 
     tcg_rt = cpu_reg(s, rt);
@@ -2119,6 +2148,7 @@  static void disas_ldst_reg_imm9(DisasContext *s, uint32_t insn,
         is_store = (opc == 0);
         is_signed = extract32(opc, 1, 1);
         is_extended = (size < 3) && extract32(opc, 0, 1);
+        disas_ldr_update_isyn_sse_sf(s, size, is_signed, opc);
     }
 
     switch (idx) {
@@ -2238,6 +2268,7 @@  static void disas_ldst_reg_roffset(DisasContext *s, uint32_t insn,
         is_store = (opc == 0);
         is_signed = extract32(opc, 1, 1);
         is_extended = (size < 3) && extract32(opc, 0, 1);
+        disas_ldr_update_isyn_sse_sf(s, size, is_signed, opc);
     }
 
     if (rn == 31) {
@@ -2321,6 +2352,7 @@  static void disas_ldst_reg_unsigned_imm(DisasContext *s, uint32_t insn,
         is_store = (opc == 0);
         is_signed = extract32(opc, 1, 1);
         is_extended = (size < 3) && extract32(opc, 0, 1);
+        disas_ldr_update_isyn_sse_sf(s, size, is_signed, opc);
     }
 
     if (rn == 31) {
@@ -2354,6 +2386,11 @@  static void disas_ldst_reg(DisasContext *s, uint32_t insn)
     bool is_vector = extract32(insn, 26, 1);
     int size = extract32(insn, 30, 2);
 
+    /* Vectored load/stores do not include an Insn Syndrome.  */
+    s->isyn.dabt.valid = !is_vector;
+    s->isyn.dabt.sas = size;
+    s->isyn.dabt.srt = rt;
+
     switch (extract32(insn, 24, 2)) {
     case 0:
         if (extract32(insn, 21, 1) == 1 && extract32(insn, 10, 2) == 2) {
@@ -2660,6 +2697,21 @@  static void disas_ldst_single_struct(DisasContext *s, uint32_t insn)
 /* C3.3 Loads and stores */
 static void disas_ldst(DisasContext *s, uint32_t insn)
 {
+    uint32_t isyn32;
+
+    /* Insn Syndrome in AArch64 is only valid for:
+     * Load/Stores of a single GPR (e.g not vector regs).
+     * Including register 31.
+     * Including Acquire/Release.
+     * Excluding Exclusive accesses.
+     * Excluding accesses with writeback.
+     *
+     * We clear the insn syndrome state here (invalidating it).
+     * The various sub decoders will then fill out information
+     * as they decode it.
+     */
+    memset(&s->isyn, 0, sizeof s->isyn);
+
     switch (extract32(insn, 24, 6)) {
     case 0x08: /* Load/store exclusive */
         disas_ldst_excl(s, insn);
@@ -2685,6 +2737,14 @@  static void disas_ldst(DisasContext *s, uint32_t insn)
         unallocated_encoding(s);
         break;
     }
+
+    /* The saved insn syndrome state in insn_start is already zero (invalid).
+     * We only update it if we have a valid insn syndrome to save.
+     */
+    if (s->isyn.dabt.valid) {
+        isyn32 = arm_encode_dabt_isyn_u32(&s->isyn);
+        tcg_set_insn_param(s->insn_start_idx, 2, isyn32);
+    }
 }
 
 /* C3.4.6 PC-rel. addressing
@@ -11087,7 +11147,8 @@  void gen_intermediate_code_a64(ARMCPU *cpu, TranslationBlock *tb)
     tcg_clear_temp_count();
 
     do {
-        tcg_gen_insn_start(dc->pc, 0);
+        dc->insn_start_idx = tcg_op_buf_count();
+        tcg_gen_insn_start(dc->pc, 0, 0);
         num_insns++;
 
         if (unlikely(!QTAILQ_EMPTY(&cs->breakpoints))) {
diff --git a/target-arm/translate.c b/target-arm/translate.c
index cf3dc33..0d53e7d 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -11349,7 +11349,8 @@  void gen_intermediate_code(CPUARMState *env, TranslationBlock *tb)
       }
     do {
         tcg_gen_insn_start(dc->pc,
-                           (dc->condexec_cond << 4) | (dc->condexec_mask >> 1));
+                           (dc->condexec_cond << 4) | (dc->condexec_mask >> 1),
+                           0);
         num_insns++;
 
 #ifdef CONFIG_USER_ONLY
@@ -11665,8 +11666,10 @@  void restore_state_to_opc(CPUARMState *env, TranslationBlock *tb,
     if (is_a64(env)) {
         env->pc = data[0];
         env->condexec_bits = 0;
+        arm_decode_dabt_isyn_u32(&env->isyn, data[2]);
     } else {
         env->regs[15] = data[0];
         env->condexec_bits = data[1];
+        arm_decode_dabt_isyn_u32(&env->isyn, data[2]);
     }
 }
diff --git a/target-arm/translate.h b/target-arm/translate.h
index a94e17e..2130a84 100644
--- a/target-arm/translate.h
+++ b/target-arm/translate.h
@@ -58,6 +58,9 @@  typedef struct DisasContext {
     bool ss_same_el;
     /* Bottom two bits of XScale c15_cpar coprocessor access control reg */
     int c15_cpar;
+    ARMInsnSyndrome isyn;
+    /* TCG op index of the current insn_start.  */
+    int insn_start_idx;
 #define TMP_A64_MAX 16
     int tmp_a64_count;
     TCGv_i64 tmp_a64[TMP_A64_MAX];